Directions

In a deep skillet, melt 1 tablespoon of the butter with the olive oil. Add the onion,cover and cook over high heat, stirring once of twice until softened, about 5 minutes. Uncover and cook over medium-high heat, stirring occasionally, until the onion is tender and caramelized, about 25 minutes. Add water to the skillet as necessary to prevent onion from scorching. Season with salt and pepper.

Spread bread with remain butter and arrange, buttered side down, on work surface. Spread a thin layer of mustard on each slice. Top half of the slices with onion, Gruyere and pickles.

Preheat skillet or panini press. Grill sandwiches over low heat until bread is toasted and cheese is melted. Cut in half and serve.